1. Field of the Invention
The invention relates to cementitious compositions which set on admixture with water and particularly to a method for controlling the temporal interval between mixture of the compositions with water and the setting thereof.
2. Description of the Prior Art
Mortar compositions have long been used for construction purposes, those mortar compositions presently in use usually containing portland cement and aggregates which harden on addition of water. Portland cement compositions are hydraulic in nature, that is, such compositions are capable of hardening under water or when not in the presence of air. On addition of water to hydraulic cement compositions, a process known as "hydraulic hydration" occurs, the composition hardening as a result of this hydration. According to present practices, additive compositions are known which are primarily used to strengthen hydraulic cement compositions. Additive compostions are also known which retard or accelerate the setting of hydraulic cement compositions. However, retarding compositions have not been greatly effective due to the unpredictability of their behavior, certain cement compositions being completely inhibited from hydration when such additive compositions are utilized. It has not been possible, therefore, according to prior art practices to controllably retard the setting of mortar compositions, particularly hydraulic cement compositions, in a manner which allows holding of mortar in a plastic, workable state for any extended period of time and still retain the capability of immediate setting of the mortar when the mortar is actually used at some time during this holding period.
Additives previously used in the formulation of mortar include agents which act to strengthen the mortar, entrain air in the mortar, plasticize the mortar, color the mortar, and vary setting times of mortars. As disclosed by Kelly et al in U.S. Pat. No. 3,432,317, saccharide polymers inter alia are added to cementitious materials in order to strengthen the hardened mortar. The saccharide polymers so disclosed provide a strengthening function without retarding the setting rate of the mortar according to the invention disclosed by Kelly et al. It is noted in the aforesaid patent that sugars, such as the glucosaccharides of the patent, are retarders of cement hydration and are unpredictable in use. Therefore, the teachings of Kelly et al do not provide an additive for or a method for controlling the setting of a cementitious material, particularly a hydraulic cement, which allows a hydraulic mortar to be formed and held for an extended period of time.
In U.S. Pat. No. 3,432,316, Kelly et al disclose the addition of extracts or portions of the tobacco plant to hydraulic cement in order to increase the strength of the concrete formed thereby and to cause a degree of retardation of hardening of the cement. Kelly et al do not disclose a method for maintaining a hydraulic mortar mixture in a plastic, workable condition for an extended period of time. Kelly et al further do not disclose a method for utilizing a mortar mixture which has been or can be maintained in a plastic, workable condition for an extended period of time and which can be used at any time during this extended period of time with the mortar mixture setting up as rapidly or more rapidly than normally on application of said mortar mixture to brick, block, or the like.